1. Field of the Invention
The invention relates to video insertion techniques in cathode ray display systems. More particularly, the invention relates to the precision gain balancing of two video sources so that by video insertion techniques the two may be combined into a single display without alerting the viewer that a video insertion has taken place.
2. Description of the Prior Art
In simulator training devices, much use is made of scale models. A gantry-mounted optical probe is maneuvered about the scale model in accordance with the manner in which a trainee manipulates the controls of the simulator trainer device. A typical scale model will include an airport and the territory surrounding it. For greatest training purposes, an existing airport and the terrain peculiar to that airport are carefully reproduced on the scale model board. In this manner a trainee learning to fly an aircraft becomes familiar with the airfield approaches at the same time as he learns to handle the controls of the particular aircraft simulated.
In certain instances where training, taxiing, and maneuvering among other aircraft parked at the airport may be required, significant detailing of the airport, its buildings, and the various parked aircraft is required. In such instances two model boards are usually provided. One at a scale which will allow the trainee to view the airport and its surrounding terrain and the other model, built to a larger scale, showing the airport itself in greater detail. Two model boards are used since it would be impractical in terms of expense and space requirements to produce a single model board in sufficient detail and of large enough scale to detail the airport area and include enough of the surrounding terrain to give sufficient training in flying above that terrain.
A similar situation will arise in the case in which the trainer simulates a spacecraft. If one considers the scene viewed by the astronaut-pilot of an incoming spacecraft, it will be realized that a large sector of the surface of the earth will be in view as the astronaut maneuvers his craft to reduce the energy of his fall. The closer the astronaut comes to the earth, the smaller is the sector of earth that he views. Eventually his landing site will become discernible and he will target-in on that area and make his landing approach and touch-down at the designated site.
In terms of camera models, it will be obvious that the model depicting the view from space, that large sector of earth viewed by the astronaut, will require relatively little detail. However, the landing site itself must provide significantly greater detail to guide the astronaut pilot to a safe landing as he approaches closer to the ground. Thus, a second model board of the designated landing site built to a significantly greater scale than that of the vast sector of earth depicted in the first model board, is required in order to guide and train the astronaut-pilot in his landing maneuver.
Although the two situations set forth above are similar in that they each require at least two model boards to be utilized with the simulator trainer, the problems presented, in effectively implementing such training, are quite different. For example, a typical ploy for shifting a pilot's presentation from the small scale, low detail model of the airport and its environs is to allow the trainee to begin a normal approach to the airport. However, it may be conveniently arranged that a simulated cloud bank must be traversed as he comes closer to the airport. As the trainee apparently enters into the cloud bank, the camera probe, which is not then presenting scale model information to the trainee, is moved over and above the large scale, high detail model of the airport itself. Thus, as the pilot breaks from the clouds he finds himself still on his approach path and in clear sight of the airport, which he sees in great detail.
When an astronaut is piloting his craft on its return flight to earth the designated landing site begins to assume significant detail while the aircraft is still at such an altitude that the surrounding terrain forms a significant part of the pilot's field of view. This requires the continual insetting of details from the large scale, landing-site model rather than merely making a single transition from one scale model to the next. As the spacecraft continues its descent, the landing site assumes a greater proportion of the image presented to the astronaut-pilot, the environs assuming less importance as the pilot concentrates on his landing site. Eventually an altitude is reached at which only the designated landing site fills the pilot's field of view. At this time no further insetting is required and only the greatly detailed, high scale model of the landing site is required.
Since there is a continual process of insetting the image of the highly detailed landing site within the image of the high altitude, low detail model, it is impractical to consider the use of a conveniently simulated cloud layer to disguise the imagery transition. Such trickery would become readily apparent to the trainee-operator of the simulator. The problem, therefore, is to enable the continual insertion of a detailed image of the landing site into the display presented to the astronaut-trainee in such a manner that no visual "glitches" are presented to the astronaut so as to distract him or impair the sense of reality sought to be created within the simulator environment.
Television viewers have been aware of insetting techniques for some time. This occurs when a picture appears in one corner of the TV presentation while the main scene continues to be played on the balance of the screen. However, there are other instances in which commercial television stations make use of insetting techniques and the viewer is unaware that part of the picture he is viewing is produced by an inset. Often this latter technique is employed when the entertainer being viewed on TV appears to enter into a model stage set much smaller than the entertainer himself. Frequent use of this technique is made in advertising in which the product advertised appears larger-than-life and dwarfs the individual on the screen who is advocating the use of the product being advertised.
In a simulator environment there may be no sharp line of demarcation between the background scene and the landing site image to be inset therein, such as occurs in the examples of commercial television techniques just noted. The image inset in the simulator display must appear to blend evenly and be a part of the entire scene. The point of view from which the overall scene is observed must agree with that in which the inset image is viewed. For most effective training, the operator must be completely unaware of the utilization of any insetting whatsoever.
The smooth blending of the inset image into the overall display is especially dependent upon the gain balance in each image channel. If the gain of the inset channel is higher than that of the overall display channel, the inset will appear as a bright blotch on the display. Conversely, if the inset channel gain is too low, the entire inset image will be darker than the rest of the display.
It shall be an object of the present invention to provide a means of precision gain-balancing two video channels for use in a single display. It shall further be an object of the invention to permit switching between two video channels without noticeable brightness change.